Device for determining moisture content, density, and direction of grain of wood, and other semiconducting material



May 2, 1950 J. P. LIMBACH DEVICE FOR DETERIINING MOISTURE CONTENT, DENSITY, AND DIRECTION OF GRAIN 0F WOOD, AND OTHER SEIICONDUCTING MATERIAL s Sheets-$11951. 1

Filed Aug. 16, 1946 A Q/EO INVENTOR \LRLIMBACH ATTORBEY J. P. LIMBACH DEVICE FOR DETERMINING MOISTURE CO May 2, 1950 2,505,778 N'I'ENT, mansx'rv, AND DIRECTION OF GRAIN 0F woon,

- AND OTHER SEIIICONDUCTING MATERIAL Eiled Aug. 16, 1946 3 Sheets-Sheet 2 INVENTQR J.P. LIMBACH ATTORNEY May 2, 1950 -J. P. LIMBACH 2,505,778

DEVICE FOR DETERMINING MOISTURE CONTENT, DENSITY, AND DIRECTION OF GRAIN or WOOD,

AND 0mm SEMICONDUCTING MATERIAL Filed Aug. 16, 1946 v 3 Sheets-Sheet .3

INVENTOR J.P.LlMBACH RNEY Patented May}, 1950 DEVICE FOR DETERMINING MOISTURE CONTENT, DENSITY, AND DIRECTION OF 01mm or WOOD, AND oral-1a SEMICON- DUCTING MATERIAL John P. Limbach, Madison, Wis., dedicated to the free we of the People in the territory of the United States Application August 18, 1946, Serial No. 690,880

(Granted under the act or' March a, 1883, as

. amended April :0. 1928:8701 o. o. 151) This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government of the United States of adjacent to a flat wood surface, since all turns America for governmen al purp ut the are very close to the wood, thus concentrating payment to me of any royalty thereon. the field as close to the wood as possible. The I hereby dedicate the invention herein dedirection of the grain doesnot affect the response scribed to the free use of the people in the terof this type of coil, regardless of how the coil is ritory of the United States to take effect on the turnedupon the surface of .the wood. By spiral, granting of a patent to me. I mean winding or circling around an axis and My invention relates to the determination of gradually receding from it. moisture content, density, and direction of grain Spiral coil i is held on collar 2 by any convenwhere present, as in wood, of semiconductive tional means. Collar 2 is mounted in sleeve 8 materials by the measurement of the effect that by thumb nuts 24 and screws 25. such materials or their contained components The coil 4 shown in Figures 3 and 4 is a somehave upon a varying electromagnetic held. The what flattened solenoid or helix of insulated wire contained moistur is determined by measurewhich may be wound upon any suitable core. ment of the effect of the moisture upon a varywhich may be hollow and should be of a material ing electromagnetic field over and above the that is not responsive to moisture changes. The effect produced upon this field by the material solenoid may be encased in a resin, eliminating itself. The density of semiconductive materials v the need for a core. The coil of Figures 3 and 4 is determined'by a measurement or comparison is used for the measurement of the direction of of the effect of these materials upon a varying grain of materials. -In Figure 4 the solenoid is electromagnetic field when such materials are 2 shown mounted on an indicator bar 5 which is either free from moisture or are at a relatively p d at 6 119011 the Strip S p 1 is 1 low moisture content, in which case the mols fl ly m unted, by means of groov 8 nd P n ture content is suitably compensated for. The upon T-head l0 which fits against an edge of direction of grain of a semiconductive material, the board in tested. Attached tolor ,insuch as wood, is determined by a measurement 3o with S p 1 is an a e indicating ole of the difference of the efiect of a unidirectional w reby the a e between the wires and the varying electromagnetic field upon such mated of e m al y b termined. rials or their contained components when the The electrical circuit disclosed in Figures 5 and grain direction of these materials is oriented in 7 c mp ises a vacuum tube oscillator ondyvaeuum different directions with respect to the direction 35 who me er- The left half of vacuum tube It of t electromagnetic fie1d (1G6GTG) drives the oscillatory circuit com- I attain these objects by the apparatus illuspo ed of the 13.3 microhenry coil H and 040 trated in the accompanying drawing, in which micromicrofarad trimmer condenser ii. The Figure 1 is a spiral coil; Figure 2 is a vertical right ha f of the tube acts as a vacuum tube section of an apparatus for mounting the spiral 4o voltmeter to detect and indicate a change in the coil above the material under test; Figure 3 illus- Oscillator 0011 when Placed near 11080101118 g t t type f (3011 t t is used to measure material such as wood. The inductance of the direction of grain of materials; Figure 4 is a plan coil may v y over a de range. sug ested view of t coil 1 Figure 3 pivotally mounted values for the other elements shown in Figure over the board being tested; Figures -5 and 6 5 '7 are as follows: A 500,000 ohm resistor It and illustrate two circuits that may be used in con- :1 1.5 volt cell It are connected across the 0-150 junction with the coils; and Figure 7 is a modimieroampmeter I t fi me t-plate cirncati f th ir t of Figure 5, cult are a volt battery is and a 50,000 ohm The coil i shown in Figure 1 comprises a single resistor 20. Resistor 2| is 100,000 ohms. Resistor spiral of insulated w1re This c011 may be flat, 5 22 1S 2 megohms. The filament cell 23 15 1.5 V0105. for application to flat surfaces, or it may be bent These values are optional and the circuit may or shaped to conform to other surfaces. It may be re-designed according to well kn w prinbe applied directly to the surface of the material ciples. under examination or it may be supported above Figure 6 is a resonance type circuit which is the material at a known or definite distance as '55 coupled to a radio frequency oscillator. The cir- 4 Claims. (0!..175-183) shown in Figure 2. 0011 I is used to determine moisture content and density of semiconducting materials. This flat, single-thickness coil is designed to give a maximum response when placed 3. euit comprises a 13.3 microhenry coil ll shunted by -30 micromicrofarad trimmer condenser ll. Resistor I6 is 500,000 ohms. The meter indicates 0-150 microamps.

The manner in which the instrument is empioyed will now be described.

Determination 0/ the moisture content of semiconducting materials While contained moisture is a very large factor contributing to the effect that a semiconducting material has upon a varying electromagnetic field, the nature of the substance itself is also such a factor. For this reason it is necessary, when determining the moisture content of these substances, to subtract from the total effect of the substance with its contained moisture, the effect of the substance alone. This implies a correction factor for each different substance, and in fact even different types of the same sub stance such as the various species of wood.

Regarding even the same species of wood, the field Ls affected by the density of such wood. In most cases the effect of density within a species of wood is relatively slight as compared to the effect which any appreciable amount of contained moisture has upon a varying electromagnetic field, with the result that it is justifiable to assume an average density for a species and determine moisture contents on the basis of this assumed average density. Any errors due to reasonable variations from this assumed average value of density are negligible when determining appreciable moisture contents.

The procedure for calibrating the meter of the device to read moisture content values of Douglasfir between the limits of 6 percent and percent is as follows:

1. Obtain a number of specimens of typical Douglas-fir of average density and condition some of these to, let us say, 6 percent, some to 12 percent, some to 18 percent, some to 24 percent, and the remainder to 30 percent moisture content.

2. Place the detection unit of the device upon the 6 percent moisture content specimens, note the deflection of the meter, and calibrate it as the 6 percent moisture content point.

3. Repeat the above process with the 12, 18, 24, and 30 percent moisture content specimens.

4. Interpolate between calibrated points for intermediate values and draw the moisture content scale.

The device thus calibrated is ready for use in the determination of the moisture content values of Douglas-fir. In use, the detection unit is placed uopn the Douglas-fir under examinaton and the calibrated dial read directly in moisture content values.

Meter dials for the determination of moisture content values of other species of wood or of other materials are prepared in a similar manner.

Determination of the dens'tu o, semiconducting materials While the effect of the contained moisture of a material upon a varying electromagnetic field is great, determination of density of such materials can be made nonetheless by applying a procedure similar to that given below for balsa.

Procedure for determining the density of balsa by means of a varying magnetic field 1. Obtain a uniform low-density specimen of balsa.

" 2. Carefully determine the density of this spec- 4 imenbystandardmethodssuchasweighinsand measuring when at a known moisture content or when oven dry. This specimen will hencefigtchh be referred to as the low-density master 3. Obtain a uniform medium density specimen of balsa.

4. Carefully determine the density of this specimen by a standard method. This specimen will henceforth be referred to as the medium-density master block."

5. Obtain a uniform high-density specimen of balsa of uniform density throughout its length, width. and thickness.

6. Carefully determine the density of this specimen by a standard method. This specimen will henceforth be referred to as the "high-density master block.

7. Condition all three of the master blocks along with the material to be checked for density so that the master blocks and the material will be at the same percent moisture content.

8. when the master blocks and the material to be checked for density are at a uniform and relatively low percent moisture content, calibrate the meter of the measuring device in terms expressing density by means of the master blocks.

(The coil is set upon the low-density master block and the meter reading is calibrated for the known value of density of this master block. The process is repeated for the medium and high-density master blocks and intermediate calibrations are interpoiated.)

9. Proceed to read the density values of the material to be checked for density by setting the coil upon the material under examination and reading the calibrated meter of the measuring device.

The foregoing procedure regarding balsa is illust-rated merely to demonstrate a method of applying a varying electromagnetic field for the determination of the density of a relatively large quantity of a material and it is to be understood that similar methods apply as well to other semiconducting materials.

Determination of the direction 0/ grain of semiconducting materials Any semiconducting material having unidirectional elements such as fibers or pores can be examined for the direction of these elements by its inspection under a unidirectional varying electromagnetic field. Such a field may affect the elements of the material to a greater or lesser extent depending upon their orientation with respect to the fied. hence a measure of the effect on the field can be used as an indication of the orientation of such elements. Frequently, the application of slight amounts of moisture or other conducting substance to the surface of such a material increases the selective effect of the unidirectional elements by reason of the orientation of the moisture or other conducting substance in the direction of such elements.

with wood, the field is least affected when the direction of the fibers is the same as the direction of the wires of the coil winding (see Fig. 4) and most affected when the direction of the fibers is at right angles to the direction of the coil winding, hence a typical procedure in determining the direction of grain of a piece of wood would be as follows:

1. Place the electromagnetic coil upon the surface of the wood and orientate it until its field isthe'least affected bythewoodasshown. fa

, example. by a minimum ammeter deflection in circuitinllgurelia. (Ininstanceswherethewood is unpainted. the surface may be dampened with moisture or with some other conducting substance before inspectionto augment the selective effect of the field.)

2. when it is desired to determine the angle that the grain direction makes with the edge of the material it is required to determine theangle the wires of the coil make with the edge of the material. This can be readily accomplished with equipment such as that shown in Figure 4.

Radio frequencies in the broadcast frequency range can be used. Audio, super-sonic and higher frequencies may also be.used.

Having thus described my invention, I claim:

1. An apparatus for dete ng the direction of grain in wood comprising a helical inductance coil adapted to be placed on or adjacent to the surface of the material to be tested, a circuit connected to said coil to impress a predetermined high frequency alternating electric current through said coil, means for pivotally supporting the coil for rotation over the surface of the wood about an axis perpendicular to the longitudinal axis of the helix, the longitudinal axis of the helix being disposed longitudinally to the surface of the wood, means indicating the angle through which the coil is rotated, means connected to said high frequency alternating current circuit to indicate a change in the current as the coil is ro-v tated.

2. The apparatus defined in claim 1 in which the inductance coil is a helical coil of flattened cross-section mounted upon an indicator bar, said bar being pivotally mounted upon a strip, so that the bar and coil may be rotated about an axis graininwoodcomprisingplacingaheliealinductance coil on or adjacent tothe surface of the wood, the longitudinal axis of the helix being disposed longitudinally to the surface of the wood, impressing a high frequency alternating current upon the coil, indicating a function of the current, turning the coil about an axis transverse to the longitudinal axis of the coil and transverse to thesurface of the wood until the indicator shows an inflection point in said current function.

4. An apparatus for determining directional physical properties of a material comprising a flattened helical inductance coil adapted to be Placed on or adjacent to the surface of the material to be tested, a circuit connected to said coil to impress a predetermined high frequency electric current through said coil, means for pivotally supporting the coil for rotation over the surface of the said material about a pivotal axis that is perpendicular to the longitudinal axis of the helix,

the longitudinal axis of the helix and the planes of the flattenedsurfaces of the coil being disposed longitudinally to the surface of the material, means indicating the angle through which the coil is turned about said pivotal axis, means connected to said high frequency circuit to indicate a change in the current as the coil is turned about the pivotal axis.

JOHN P. LIMBACH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re.21.711 Blake Feb. 11, 1941 1,708,074 Allen Apr. 9, 1929 1,780,952 Symes Nov. 11, 1930 1,943,619 Mudge et al. Jan. 16,1934 2,023,228 Hermann Dec. 3, 1935 2,231,035 Stevens et al Feb. 11, 1941 2,308,566 Noxon Jan. 19, 1943 2,326,344 Elmendori' et al. Aug. 10, 1943 2,389,190 l 'ermier Nov. 20, 1945 Certificate of Correction Patent No. 2,505,778 May 2, 1950 JOHN P. LIMBACH It is hereby cert'fied that error appears in the above numbered patent requiring correction as follows:

In the grant, lines 1 and 14, name of inventor, for Joseph P. Limbach read John P. Limbach;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 3rd day of October, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction May 2, 1950 Patent No. 2,505,778

JOHN P. LIMBACH It is hereby certified that error appears in the above numbered patent requiring correction as follows:

In the grant, lines 1 and 14, name of'inventor, for Joseph P. Limbac read John P. Limbach;

and that the said Letters Patent should be read as corrected above, so that the same 7 may conform to the record of the case in the Patent Office.

Signed and sealed this 3rd day of October, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assistant Gammissz'oner of Patents.

Certificate of Correction Patent No. 2,505,778 May 2, 1950 JOHN P. LIMBACH It is hereby certified that error appears in the above numbered patent requiring correction as follows:

In the grant, lines 1 and 14, name of inventor, for Joseph P. Limbach read John P. Limbach;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 3rd day of October, A. D. 1950.

[sur] THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

